Excess air burner

ABSTRACT

A GAS BURNER PARTICULARLY ADAPTED FOR OPERATION WITH EXCEPTIONALLY LARGE QUANTITIES OF EXCESS AIR. THE PREFERRED EMBODIMENT OF THE BURNER COMPRISES A GENERALLY CYLINDRICAL, CERAMIC BURNER BLOCK HAVING A CENTRAL BORE WHICH INCREASES IN DIAMETER NON-UNIFORMLY FROM THE INLET TO THE OUTLET. THE GAS INLET COMPRISES A TUBE MEMBER POSITIONED AXIALLY OF THE BORE AND TERMINATING CLOSELY ADJACENT THE INLET END. A CIRCULAR FLANGE EXTENDS OUTWARDLY ABOUT THE END OF THE TUBE INTO CLOSE PROXIMITY WITH THE BORE TO DEFINE A NARROW ANNULAR GAP OR SPACE. AIR IS SUPPLIED ANNULARLY OF THE TUBE AND FLOWS THROUGH THE NARROW GAP WITH SUBSTANTIAL VELOCITY. THIS CAUSES A VACUUM ACROSS THE FACE OF THE FLANGE AND GAS SUPPLY TUBE TO PRODUCE GOOD MIXING EFFICIENT COMBUSTION. BY PROPERLY RELATING THE SIZE OF THE FLANGE, THE ANNULAR OPENING AND THE BORE, THE   BURNER GIVES EXCELLENT COMBUSTION CHARACTERISTICS THROUGHOUT SUBSTANTIAL VARIATIONS IN GAS-AIR RATIOS.

July 11, 1972 SELLORS, JR" ETAL 3,676,048

EXCESS AIR BURNER Filed March 13, 1970 2 Sheets-Sheet 1 INVENTORS.

JOHN ELLORS,JR. H RD E. SHULAR Wyn, 5%

ATTORNEYS.

United States Patent 3,676,048 EXCESS AIR BURNER John Sellors, Jr., andHoward E. Shular, Cleveland, Ohio,

assignors to Pyronics Inc., Cleveland, Ohio Filed Mar. 13, 1970, Ser.No. 19,305 Int. Cl. F23d /02 US. Cl. 431-353 1 Claim ABSTRACT OF THEDISCLOSURE A gas burner particularly adapted for operation withexceptionally large quantities of excess air. The preferred embodimentof the burner comprises a generally cylindrical, ceramic burner blockhaving a central bore which increases in diameter non-uniformly from theinlet to the outlet. The gas inlet comprises a tube member positionedaxially of the bore and terminating closely adjacent the inlet end. Acircular flange extends outwardly about the end of the tube into closeproximity with the bore to define a narrow annular gap or space. Air issupplied annularly of the tube and flows through the narrow gap withsubstantial velocity. This causes a vacuum across the face of the flangeand gas supply tube to produce good mixing and efficient combustion. Byproperly relating the size of the flange, the annular opening and thebore, the burner gives excellent combustion characteristics throughoutsubstantial variations in gas-air ratios.

The present invention is directed toward the fuel burner art and, moreparticularly, to an improved gas burner.

The invention will be described with particular reference to a burner ofthe type generally referred to as an air preheater or excess air burnerand will be described with particular reference thereto; however, itwill be appreciated the invention is capable of broader application andcould be used in a variety of different burner types.

One of the commonly used gas burners comprises a a ceramic burner blockwhich is cemented into a cast iron holder. A cage extends rearwardlyfrom the holder and a blast burner nozzle is positioned therein. Agas-air mixture is supplied to the nozzle and burned with additional airinduced through the cage.

The general type of burner described is manufactured with variety ofspecific internal structures and configurations. Various blast nozzleshave been used and air has been supplied to the units at atmosphericpressure, as well as, at substantial positive pressure. With all of theprior structures, there have been problems. For example, there have beendifliculties in obtaining high turn down ratios. Likewise, there havebeen problems in providing burners which could operate efliciently inhigh velocity air streams. Problems with the burners requiring extensivewarm-up time have also been prevalent.

In general, attempts to overcome these problems have resulted inincreasingly complex and costly burners. Additionally, the burners haverequired increasingly complex controls and have not been particularlysuitable for use in a variety of environments.

The present invention provides a gas burner which overcomes the aboveproblems and is extremely simple in construction. Additionally, burnersformed in accordance with the invention are capable of operationthroughout a high turn-down range and with either constant or variableairflow.

In accordance with the invention there is provided a gas burnerespecially suited for operation with substantial amounts of excess air.According to the invention the burner comprises a burner block memberhaving a central bore extending therethrough and increasing incross-sec- 3,676,048 Patented July 11, 1972 tion from an inlet end to anoutlet end. A tubular gas supply member extends axially into the inletend. Air supply means are connected to the inlet end for supplying airto the bore annularly of the tubular gas supply member. Extendinggenerally radially outwardly of the end of the tubular member is animperforate flange member which has its outermost peripheral edgeclosely spaced from the innerwall of the inlet end of the bore. The airis thus caused to exit at substantially velocity about the end of thetubular gas supply member in a manner which produces a low pressure orvacuum across the face of the flange. The relationship of the disc tothe bore and the tubular member is such as to provide extremely goodgasair mixing and stable combustion throughout a wide range of firingrates and gas-air ratios.

In accordance with a more limited aspect of the invention, the bore hasa non-uniform or stepped cross-section which further enhances mixing andcombustion.

Accordingly, a primary object of the invention is the provision of ahighly simplified gas burner which can operate throughout a highturndown range.

Another object is the provision of a gas burner which can operatethroughout a wide range with air supplied at constant velocity.

Yet another object is the provision of a gas burner which requiressubstantially no warm-up time.

A still further object of the invention is the provision of a burnerwhich can operate efficiently with up to as much as 3000 percent excessair.

Still another object is the provision of an excess air burner which canproduce flue gas temperatures from 2500 F. and higher to as low as 250F.

Yet a further object is the provision of a burner which can produce awide range of precisely controllable temperatures with a substantialconstant volume of hot gas output.

A further object is the provision of a gas burner which has the abovementioned operational characteristics with an extremely simple internalstructure.

These and other objects and advantages will become apparent from thefollowing description when read in conjunction with the accompanyingdrawings wherein:

FIG. 1 is a cross-sectional view through a preferred embodiment of thepresent invention;

FIG. 2 is a cross-section taken on line 2-2 of FIG. 1;

FIG. 3 is an enlarged cross-sectional view showing the air and gas inletportion or throat of the FIG. 1 embodimerit;

FIG. 4 is a longitudinal cross-section through a modified burner formedin accordance with the invention; and

FIG. 5 is a cross-sectional view taken on line 5-5 of FIG. 4.

Referring more particularly to FIG. 1, it will be seen that thepreferred form of the invention comprises a burner including a burnerblock or combustion chamber forming section A and an air-fuel inletsection B. In the embodiment under consideration, the burner block orcombustion chamber portion A comprises a generally cylindrical bodyformed from a high temperature refractory ceramic. A bore 12 extendslongitudinally through member 10. As can be seen, the bore 12 has acircular outlet opening 14 which connects with a uniformly taperingportion 16 extending a substantial distance into the block 10. A smallerdiameter tapered portion 18 is joined through a truncated chronicaltransition 20 with the inner end of the portion 16. The inlet end of theburner block 10 is defined by a circular opening 22 of uniform diameterwhich connects with the portion 18 by a tapered transition 24. As can beseen, the described arrangement gives the bore 12 a steppedconfiguration. A desirability of this relationship will be describedmore fully hereafter.

The burner block 10 is mounted in a block holder member 28 whichincludes a cylindrical sleeve or wall 30 which is received in a recess32 formed on the external surface of the block 10. A rear wall 34connects to the cylindrical sleeve 30 and has an outwardly extendingannular flange portion 36 which serves to mount the burner structure. Itwill be noted that the flange 36 is provided with circumferentiallyspaced mounting holes 40.

The block holder 28 is preferably formed from cast iron and joined tothe block by a cement or adhesive 42 although obviously other types ofmaterials and joining methods could be used.

The fuel air inlet portion of the burner comprises an air manifoldsection 50 which is comprised of a generally cylindrical portion 52terminating in a radially extending flange 54. The flange 54 isconnected to the end wall 34 of the block holder 28 by a plurality ofmachine screws 56. A gasket 58 is positioned within flange 54 and theendwall 34. Extending laterally from the portion 52 is the air inletsection 60 which is provided with a suitable flange 62 for connection toan air supply line 64.

Gas is supplied to the burner from any convenient source. In theembodiment under consideration, the gas is supplied through a manifold68 having an outlet opening 70 connected to the rear of the air manifold52.

Of particular importance to the invention it is the arrangement of theair and gas supply. The combination of the gas-air supply arrangementtogether with the stepped burner block provides a burner which canfunction over a wide range of gas and air ratio, and which does notrequire any warm-up time.

The preferred form of air-gas supply arrangement can best be seen fromFIGS. 1 and 3. As shown therein, the gas is supplied from manifold 68through a circular tubular member or pipe 80 which terminates inwardly ashort distance from the outer end of opening 22. The air is suppliedthrough the chamber 52 annularly about the pipe 80. At the outlet end ofpipe 80 a disc member or outwardly extending flange portion 82 ispositioned such that it is closely spaced from the inner wall of thebore thereby causing the air to flow through a narrow annular slit oropening 84. The relationship between the gas outlet opening diameter(i.e., the diameter of the opening 86) and the annular opening 84 issuch that a substantial air velocity is produced annularly about theopening 86. This produces a suction or vacuum across the face of thedisc or flange member 82 and causes mixing of the fuel and air whilesimultaneously shielding the mixture from the incoming air so as topermit it to begin combustion. The shielding effect of the disc allowscombustion to proceed a substantial amount with a full flame beingproduced across the interior of the disc.

The stepped burner bore arrangement with its somewhat sudden increase ofdiameter up to the wall 16 causes the flame to be somewhat short.Additionally the sharp diameter increase of the steps causes small eddyflames to be produced Within the steps. This eliminates the need for theblock to be heated-up prior to full or maximum operation of the burner.

The stepped design in combination with the air-gas inlet arrangementproduces extremely good flame stability throughout a Wide range offiring rates. Additionally, it is possible to operate the burner at upto 3.000% excess air.

Also of importance to one aspect of the invention is the pilot burnerarrangement. As seen in FIG. 1, a pilot or ignition opening for theburner is shown as a circular opening 88 which extends into the firststep of the bore 12. Note that the opening 88 comes in at approximatelythe juncture between the wall 24 and the wall 18. An ordinary gas pilotburner (not shown) extends into the opening for igniting the gas-airmixture supplied to the bore. Proper lighting of the mixture at all flowrates is assured by a short tab 90 which extends radially of the annularopening between pipe 80 and bore 22. As shown in FIG. 2, the tab 90 isapproximately the width of the pilot opening 88. This tab shields thepilot flame and produces a negative air pressure which, in combinationwith the stepped bore, assures proper pilot operation without regard tothe velocity within the bore 12.

The proper relationship between the gas outlet area of opening 86 andthe arrangement of the air outlet opening 84 can be foundexperimentally. One example of a burner size which is especiallyadvantageous is adapted to handle from between 50 to 1500 standard cubicfeet per hour of gas with a constant air flow of 15,000 standard cubicfeet per hour. A burner adapted for this type of operation has theopening 22 of 4% inches in diameter and the disc 82 with a diameter of3% inches. The velocity of air flow through the gap 84 is in a range ofabout 416 feet per second. The burner will operate with a variety of airflow rates of, for example, from as low as approximately 40 ft. persecond to as high as in the range of 800 ft. per second through the gap84.

The relationship of the stepped burner block is substantially lesscritical and the inlet air gas arrangement can be used in many types ofblocks; however, the relationship shown in FIG. 1 is approximately toscale and is extremely advantageous. An important feature of the steppedburner block being the creation of small eddy flames which preventquenching of the main flame on start-up and which, additionally, produceexcellent flame stability at all firing rates.

Although the embodiment shown in FIGS. 1-3 is preferred, the samegeneral type of arrangement can be used in burners having othercross-sections. FIGS. 4 and 5 show an embodiment which has a rectangularcross-section and produces a Wide flat flame. As shown, the burners inFIGS. 4 and 5 have generally the same air gas inlet arrangement andincludes a first cast housing or manifold member which has an air inletopening 102 and a gas supply inlet 104. Openings 102 and 104 areconnected to suitable supply manifolds not shown. The member 100 extendsacross the back width of the burner and is connected to a burner blockholder 106 in any suitable manner such as by a plurality of machinescrews 108. A seal member 110 is positioned between the member 100 andthe burner block holder 106.

The burner block holder 106 has a generally rectangular cross-sectionand has an outwardly extending mounting flange 112 provided with aplurality of holds 114 for receiving bolts to mount the burner.

The burner block in the FIGS. 4 and 5 embodiment has generally the samelongitudinal cross-sectional configuration as the 1-3 embodiment but isrectangular as best seen in FIG. 5. The block 116 is received in themember 106 and held therein by ceramic cement 117. As can be seen, thecenter bore of the burner block 116 is unifromly tapered from the outletend 118 to a short distance forward of the air-gas inlet end. Theair-gas inlet end includes a rectangular opening 120 having a widthwhich is substantially greater than its height.

The air-gas inlet arrangement is generally the same in function andarrangement as that described with reference to the FIGS. l-3embodiments. Note that a plurality of gas supply tubes 122 extend intothe inlet end of the bore along its transverse axis. A flange member 124extends outwardly of the terminal end of tubes 122 to form a narrow,generally annular gap 126 which extends about the inner face of theinlet end. The gap is sized to produce high air velocity therethroughand a vacuum across the face of the member 124.

The pilot for the burner is arranged in the same manner as describedwith reference to FIGS. 1-3. Note that there is a pilot burner opening128 which opens into the bore just forwardly of the inlet 120.Additionally, a tab portion 130 extends outwardly immediately behind theopening 128 to shield the pilot burner (not shown) from the incomingair.

The invention has been described in great detail sufficient to enableone of ordinary skill in the burner art to make and use the same.Obviously, modifications and alterations of the preferred embodimentswill occur to others upon a reading and understanding of thespecification and it is our intention to include all such modificationsand alterations as part of our invention insofar as they come within thescope of the appended claim.

Having thus described our invention, we claim:

1. A gas burner especially suited for operation with substantial amountsof excess air comprising:

a burner block member having a central bore extending therethrough andincreasing in cross-section from an inlet end to an outlet end;

a tubular gas supply member extending axially into the inlet end of thebore, air supply means connected to the inlet end of the bore forsupplying air to the bore annularly of the tubular gas supply member;

an imperforate flange extending generally radially outwardly of the endof the tubular member, said flange member having its outermostperipheral edge closely spaced from the innerwall of the inlet end ofthe bore whereby the air is caused to exit at substantial velocity aboutthe end of the flange member in a man- 6 her which produces a lowpressure area across the face of the flange and the outlet end of saidgas supply member;

a pilot burner port formed through said burner block and opening intosaid bore adjacent said flange member in a direction toward said outlet;and

a bafile member aligned with said port and extending between said flangeand the wall of the inlet end of said bore.

References Cited UNITED STATES PATENTS 2,368,370 1/1945 Maxon 431-353 X2,375,625 5/1945 Conway 431-187 X 3,368,605 2/1968 Reed 431-3533,529,917 9/1970 Hindenlang 431351 CARROLL B. DORITY, IR., PrimaryExaminer US. Cl. X.R.

